Communications equipment keyboard



Jan. 3, 1967 c. H. CLARK ETAL 3,296,369

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COMMUNICATIONS EQUIPMENT KEYBOARD Original Filed April 5, 1962 14Sheets-Sheet 11 j j INVENTORS CLAYTON H. CLARK DONALD J JTEFAN/K BY WMATTORNEYS Jan. 3, 1 967 c. H. CLARK ET Al.

COMMUNICATIONS EQUIPMENT KEYBOARD l4 Sheets-Sheet 12 Original FiledApril 3, 1962 INVENTORS CLAYTON H. CLARK DONALD J. STEFAN/K gmfiymrm (wW ATT RNEYS 14 Sheets-Sheet 13 I 0,. O 5km 5 O M m mmm 7 ma MW 7. E w W1 11 W H5 w w I n MU T D Y m W C MN dL. 6 5 o 4 m w m 00 W Jan. 3, 1967c. H. CLARK ETAL COMMUNI CATIONS EQUIPMENT KEYBOARD Original Filed April5, 1962 1M1 s 3 436s 435 jam. 3, 1967 c CLARK ET AL 3,296,369

COMMUNICATIONS EQUIPMENT KEYBOARD Original Filed April 5, 1962 14Sheets-Sheet 14 m Q "SPACE" d P R4940 494 b INVENTORS CLAYTON H. CLARKDONALD J STEFAN/K M ymf/m 7/ ffmag/i 6w ATT RNEYS United States Patent3,296,369 COMMUNICATIONS EQUIPMENT KEYBOARD Clayton H. Clark, Mundelein,and Donald J. Stefanik,

Berwyn, Ill., assignors to SCM Corporation, New York, N.Y., acorporation of New York Original application Apr. 3, 1962, Ser. No.184,820. Divided and this application Aug. 23, 1965, Ser. No. 481,797

18 Claims. (Cl. 178-17) This invention relates to a communicationsequipment keyboard primarily intended for use in telegraphiccommunication, although it may be adapted for use with other dataprocessing applications. It particularly relates to an encodingkeyboard. This application is a division of co-pending applicationSerial No. 184,820, filed April 3, 1962.

This equipment was developed to serve a telegraphic station use whichrequire two or more interconnected teletypewriter sets with provisionfor utilizing simultaneous sending and receiving.

Various new concepts of mechanism and operation are incorporated in asmall keyboard having keys arranged with standard typewriter spacing andconstruction in a weatherproof manner to the maximum feasible extent.

Accordingly, a primary object resides in the provision of a novelcomplete encoding keyboard transmitter unit.

A further object resides in the provision of a novel weatherproofedkeyboard construction.

A further object resides in providing a novel keyboard structure inwhich the keyboard is arranged, and cooperates with the keyboard coverstructure to provide a weatherproof unit, without adverse efiect on keyoperation.

Still another object resides in the provision of a novel mechanicalkeyboard structure in which the key plates (for convenience hereinafter,the multiple leg, key plates may be referred to as key levers, althoughin a true technical sense they are not levers) are obtained fromidentical basic stampings, enabling reduced manufacturing andreplacement costs.

A still further object resides in the provision of a novel mechanicalkeyboard structure in which the key levers operate a group of pivotedtwo-position code bails having no neutral position, the angular positionof each code bail constituting one of two signals in each bit of amultiple bit signal combination and transferring such mechanicalpositioning by means of code bail actuated switches into an electricalswitching code combination.

In connection with the preceding object, it is a further object toprovide a novel magnetically operated reed switch for each code bail toaccomplish the code transfer from a mechanical to an electricalcondition.

In further conjunction with these objects it is also a further object toprovide in the keyboard unit, novel electronics which enables thekeyboard to generate both a parallel signal and a start-stop serialsignal representative of the selected keyboard character or function.

Still another object resides in providing a novel mechanical-electronickeyboard unit including controls for setting the operational mode of akeyboard-printer-recorder set enabling various input-Output connectionsand holding such selected mode condition together with a visualindication of the applicable mode of operation currently in progress.

A still further object resides in providing a novel keyboard encoder inwhich the selected key causes selective, magnetically actuated operationof permutated group of a plurality of glass enclosed reed contactswitches, and after a minute mechanical delay causes a sixth U-bailmagnetically actuated reed contact switch to close to provide a readoutof the encoded signal to associated key- Patented Jan. 3, 1967 ICC boardelectronics which electronically block repeated transmission of the samesignal if a key is maintained depressed.

In conjunction with the preceding object it is a further object toprovide a novel automatic electronic control permitting a two charactertyping burst, which exceeds a permitted line transmission rate, thisoperation being accomplished through a mechanical keyboard lockmechanism which holds the second of the two-character burst inmechanical storage in the keyboard code bails until the first selectedcharacter has been transmitted through the electronic circuitry.

Still another object in conjunction with the preceding two objectsresides in providing a repeat key mechanism on the keyboard structure,operating through the keyboard electronics to by-pass the electronicrepeat blocking and to permit repeated transmission of any characterwhose associated key is held down while the repeat key is held down.

Further novel features and other objects of this invention will becomeapparent from the following detailed description, discussion and theappended claims taken in conjunction with the accompanying drawingsshowing a complete set utilizing the keyboard, the keyboard,subcomponent structures, electronics and embodiments, in which:

FIGURE 1 is a perspective view of a teletypewriter set with a Unit 1 onthe left including a keyboard constructed in accord with the presentinvention;

FIGURE 2 is a plan view of the keyboard illustrating the keyarrangement, indicators and the mode control for the set;

FIGURE 3 is a block diagram illustrating the operating functions of thecomplete teletypewriter set depicted in FIGURE 1;

FIGURE 4 is a simplified schematic of a power supply circuit, one ofwhich is included with each of Units 1 and 2 in a set;

FIGURE 5 is shown on two sheets as FIGURES 5A and 5B and is a schematicillustrating the circuitry of the mode control panel on the keyboardunit and, for convenience, some components of correlated subassembliesin the teletypewriter set;

FIGURE 6 is a block diagram more detailed than FIGURE 5, illustratinggeneral electrical, electronic and mechanical components utilized inUnit 1 which includes a keyboard, a printer and a recorder together witha power supply (not shown in this figure);

FIGURE 7 includes 14 separate blocks identified by the Letters A throughP, each illustrating a basic schematic circuit corresponding to aspecific logic symbol and enabling convenient construction of theelectronics represented by the following logic diagram;

FIGURE 8 is shown on two sheets as FIGURES 8A and 8B and is a logicdiagram for the keyboard unit;

FIGURE 9 is a timing diagram for the keyboard;

FIGURE 10 is a perspective view of the Unit #1 drawer, which mounts thekeyboard, with all operating components removed;

FIGURE 11 is a rear view of the keyboard unit, removed from the #1 unitdrawer front panel and with its rear wall opened and swung down toillustrate the general arrangement of subassemblies and components whichare mounted in the keyboard unit;

FIGURE 12 is a partially broken away and partially exploded perspectiveview of the mechanical keyboard structure apart from the othercomponents of the keyboard unit seen in FIGURES 1 and 11;

FIGURE 13 is an enlarged vertical cross-section of the keyboardstructure illustrating the shape of the key plates and the manner inwhich they are mounted and cooperate with the code bails, the non-countshaft and the counter reset shaft, the reset lever itself being shown asoffset from its normal position for clarity;

FIGURE 14 is an enlarged detail view of one of the glass enclosed reedswitches and its rockably mounted code bail magnet operator;

FIGURE 15 is an end view of the reed switch and magnet operator seen inFIGURE 14;

FIGURE 16 is a detail plan view of one of the tabs used on the counterreset shaft and on the non-count shaft;

FIGURE 17 is a detail front view of the repeat key, its special keyplate assembly and the repeat switch;

FIGURES 18, 19 and 20 are fragmentary views showing details of thespacelever and space plate assembly; and

FIGURE 21 is a fragmentary view'illustrating the solenoid actuated codebail locking assembly.

GENERAL An over-all view of an exemplary teletypewriter set 100, whichuses keyboard 106, is shown in perspective in FIGURE 1. This equipmentwas initially developed for shipboard installation for use intelegraphic communication from ship-to-ship and from ship-to-shore, andaccordingly, certain aspects of weatherproofing are included in thisdisclosure.-

A complete teletypewriter. set (FIGURE 1) consists of two units, Unit 1and Unit 2. Unit 1 contains a printer 102, a keyboard unit 106, amagnetic tape recorder 108 and a power supply unit 110. The keyboardunit (see FIGURES 1, 2 and 11) consists of a cover case 116, a typingmechanism (see FIG- URE 12), keyboard electronics, a mode selectionpanel 118, mode switches and relays K1-K9 (under the mode pushbuttons),a tape recorder monitor panel 120, a character counter 122, and akeyboard-locking mechanism 123 (see FIGURES 11, 12 and 21), the covercase 116 mounting against a seal strip 124 (see FIGURE 10) on a frontwall panel 126 of the drawer 113. The mode panel subassembly 118 and aseal gasket 125 are secured to the keyboard cover case 116 by screws.Functionally, the keyboard unit also includes two tuning forkoscillators 128 which are mounted in the power supply unit 110 andprovide accurate time bases for a 60- or 100-w.p.m. sequentialtransmission by the keyboard.

A depressed typing key 130 causes the keyboard unit to generate both a5-bit, parallel signal in Baudot code and a 7-bit, start-stop, serialsignal in Baudot code.

A depressed mode pushbutton 132 causes the keyboard to switch variousinput-output connections of the set to desired operating modes and tolight the applicable mode indicating lamp 134.

The REWIND push'button 136 on the record monitor panel 120 causes thekeyboard unit to signal the tape recorder 108 to rewind its magnetictape.

In response to the signals from the recorder 108 the keyboard unit 106indicates, by lighted ones of lamps 138, the position of the tape in therecorder.

As determined by the selected mode of operation, the keyboard unit 106,as part of Unit 1, is used (1) to send coded messages through a 1200cycle tone generator 144 (see FIGURE 3) directly to the outgoing line(SEND KEYBD mode), (2) to store a message in the magnetic tape recorder108 (STORE mode), and (3) to test the printers 102 and 104 (TEST 1' andTEST 2 modes).

The 32 typing keys are arranged in a mechanical keyboard 400 (FIGURE 12)in three rows in teletypewriter order, although having typewriterspacing between keys. One to five glass-enclosed reed switch contacts146 (see FIGURE 8) (to be later fully described) close magnetically inresponse to the depression of any key to provide a parallel electricalencoding of the corresponding character. A sixth reed switch 148(universal bar switch) closes for each key depression to supply a startsignal to the associated keyboard electronic circuits. The feel of anelectric typewriter keyboard is duplicated even though there is nomechanical linkage between typing mechanism and printer. Two-charactertyping bursts that exceed the line rate of 60 or w.p.rn. arepermissible; the kyeboard lock solenoid 123 and associated mechanismholding the second character in mechanical storage until the firstcharacter is transmitted electrically. A repeat key 150 (see FIGURE 17)permits repeated transmission of any character whose associated key isheld down at the same time.

The main function of the keyboard electronics (see logic diagram ofFIGURE 8) is to convert parallel electrical signals generated by thetyping mechanism or by the recorder into the serial electrical signalsrequired by the outgoing line. The keyboard electronics are containedprincipally on two printed circuit boards 152 and 154 (see FIGURE 11)mounted in the rear wall unit 156 of the keyboard unit 106.

Seven mode pus'hbuttons 132 and seven associated lamps 134 make up themode selection panel 118 to the right of the typing keys. Thepushbuttons allow the operator to select a mode of operation for eitherUnit 1 or Unit 2. Momentary operation of a push'button causes operationof an associated switch and electrical locking of one or more associatedmode relays Kl-K9 and also lights a corresponding lamp 134 (DSl-DS7) onthe mode selection panel 118. With the pushbuttons, the operator canplace the set in the following modes:

(1) IDLE(RECEIVE): In the idle mode, the motors of both printers areoff; the RECEIVE lamp D85 is on; and the set is available for local use,for receiving from another station, or for both, simultaneously.Operation of the RECEIVE push'button places the set in the idle mode anddiscontinues all other modes except the RE- CEIVE mode. To set up anincoming call to this station, associated telegraph terminal groupequipment (not part of this invention) operates a supervisory relay inUnit 1 or Unit 2 to turn on the associated printer motor and thus placethe set in the RECEIVE mode.

(2) STORE: The STORE mode connects the parallel output of the keyboardunit 106 to the tape recorder 108 and the serial output of the samekeyboard unit 106 to the printer 102. This allows the operator to storea message prior to sending it to the outgoing line and to monito thestoring process. Operation of the STORE pushbutton places the set in theSTORE mode and lights the STORE lamp DS4. After typing the message torecord it on the magnetic tape, the operator presses the REWI-NDpushbutton 136 on the recorder monitor panel 120. This action causes thetape rec-order 108 to rewind and thus places the message on the tape ina position to be read and set to the line.

(3) NO ADVANCE: The NO ADVANCE mode duplicates the STORE mode exceptthat a blank area (used as a signal condition as will be fully describedhereinafter) is not inserted on the magnetic tape just ahead of therecorded message. This mode is used after a STORE mode has beeninterrupted to allow receipt of an incoming message on the Unit 1printer. A blank area cannot be permitted in a recorded message on thetape since the area is used by the recorder 108 to recognize the end ofa message.

(4) SEND KEYBOARD: To set up a call to the outgoing line, the operatorpresses the SEND KEYBD pushbutton. This extends a DC. supervisory groundfrom the connecting equipment to a mode switching relay (which operatesfrom and locks to the supervisory ground). The RECEIVE lamp D55 turnsoff and the SEND KEYBD lamp D31 turns on. In the SEND KEYBD mode, it ispossible to receive on Unit 1 printer 102 :or on Unit 2 printer 104 oron both printers simultaneously; the output of the keyboard does notappear on the Unit 1 printer 102 as it does during the STORE mode. Allcharacters typed on the keyboard during this mode are sent to theoutgoing line.

(5) SEND RECORD: To send from the recorder to the outgoing line duringthe SEND KEYBD mode, the operator presses the SEND RECORD pushbutton.This starts the tape recorder 103 which will send one tape recordedmessage and then stop automatically.

(6) TEST 1: The TEST 1 mode allows the operator to test the Unit 1printer by typing directly into it.

(7) TEST 2: The TEST 2 mode allows the operator to test the Unit 2printed by typing directly into it.

Over-all functional description FIGURE 3 shows the various functionalsections and associated external signaling lines of the exemplaryteletypewriter set, FIGURE 4 shows the power supply circuit and FIGURES5A and 5B viewed as a single figure show the mode panel controlcircuits.

OUTGOING MESSAGES: Since outgoing transmission depends on theavailability of remote switching equipment (not shown) the associatedequipment (not shown) will of course determine when a call can beoriginated. To request use of the outgoing line, the local operatordepresses the KEYBD SEND push button to operate switch S2 to connect amode relay K1 to the outgoing line. If the associated equipment isavailable, ground potential is applied to the outgoing line on a simplexbasis, completing a circuit for the mode panel relay K1. Relay K1 locksto the supervisory ground signaling through its relay terminals 1 and 6and lights the SEND KEYBD lamp DS-l through relay terminals 2 and 5 tosignal the operator that sending may start.

MESSAGE PREPARATION CONTROL: Control of the Unit 1 recorder 108 whilestoring a message is maintained from the Unit 1 keyboard 106 throughmode push buttons REWIND, STORE, and NO ADVANCE.

STORE: The STORE mode pushbutton, through switch S5, lights the STORElamp D84 and energizes relays K6 and K3 which (a) prepare the circuitsof the recording head windings through recorder relay KRl, (b) keep theSTORE lamp D54 lighted, (c) lock under control of contacts 2 and 5 ofthe RECEIVE mode relay K11 so that the associated equipment caninterrupt the STORE mode, and (d) as described under a following sectionentitled Recorder Logic, trigger the advance controller of the recordercircuitry through contacts 2 and 5 of relay K-6 to advance a smallamount of tape over the recording head. This blank portion of tape willact as an end-of-message signal for the first of two messages storedsuccessively. Further, the operated mode panel relays K6 and K3 (a)start the Unit 1 printer motor B1, and (b) connect the output of thekeyboard through contacts 1 and 6 of relay K3 and contacts 6 and 8 ofsupervisory relay K31 to the input of the Unit 1 printer 102 so that theprinter will monitor what is being stored.

NO ADVANCE: The NO ADVANCE mode pushbutton, through switch S6, lightsthe NO ADVANCE lamp D57 and energizes mode panel relays K7 and K3 which(a) prepare the circuits of the recording head windings, (b) keep the NOADVANCE lamp DS7 lighted, and (c) locks under control of the RECEIVEmode relay Kl-l so that the associated equipment can interrupt the NOADVANCE mode (which is an auxiliary STORE condition). Note that theadvance control of the recorder is by-passed in this mode and no blanktape is inserted ahead of the stored message. Further, the operated modepanel relays K7 and K3 (a) through contacts 2 and 5 of relay K3, startthe Unit 1 printer motor B1, and (b) through contacts 1 and 6 of relayK3, connect the output of the keyboard 106 to the input of the Unit 1printer 102 so that the printer 102 will monitor what is being stored inrecorder 108.

KEYBOARD: The keyboard 106 is always connected to the outgoing line. Assoon as the SEND KEYBD lamp DS1 lights when the SEND KEYBD pushbuttonswitch S2 is operated, associated equipment is available to ex- CJIpares the circuits of the recorder playback head windings 280 and 282,(b) lights the lamp DS6 beside the SEND RECORD pushbutton, (c) locksunder control of the supervisory ground returned over the outgoing linefrom the associated equipment and through contacts 1 and 6 of SEND KEYBDrelay K1, (d) triggers a searching operation by the recorder 108 by aground through contacts 2 and 5 of relay K9, and (e) blocks the keyboardelectrically through the same contacts 2 and 5 of relay K9 andassociated keyboard circuitry so that the keys cannot supply a charactereven it operated by mistake. In searching, the recorder 108 advances themagnetic tape over the head but does not send to the outgoing line untila character is found on the tape.

OUTGOING SIGNALING: A lZOO-cycle, free-running multivibrator supplies amark tone on the outgoing line with the spacing pulses provided byturning oil the multivibrator for a time controlledv by a tuning forkoscillator frequency standard. The frequency standard drives a 3-stagecounter, the output of which turns the multivibrator on and off in aseries of marks and spaces determined by the Baudot code of the desiredcharacter. Characters are supplied either by depressing a keyboardtyping key or by causing the recorder 108 to move a character stored onmagnetic tape past the recorder head playback windings 280 and 282.

Mode circuit operation FIGURE 3 shows the mode panel and its associatedcircuits in schematic form. The following theory explanation shows howthe relays of the mode panel switch the various internal and externalconnections of the teletypewriter set under control of both theassociated equipment (not shown) and the local operator.

IDLE CONDITION: With no incoming or outgoing trafific, all mode panelrelays K1 through K9 are released, and the two supervisory relays K11and K1-2 for printer 102 are released. Motor B2 control relays KZ-l andK22 are also released and the printer driving motors B1 and B2 are off.Further, incoming line relays K3-1 and K3-2 are released. The RECEIVElamp DSS is lighted during the idle condition through the followingcircuit: negative 28 volts through lamp DSS, contacts 8 and 6 of relayK7, contacts 8 and 6 of relay K6, contacts 8 and 6 of relay K5, contacts8 and 6 of relay K2, normally closed contacts of the NO ADVANCE, STORE,TEST 2 and TEST 1 switches, pin W of P11-I1l, pin 3 of P7-J7, contacts 5and 2 of relay K1-1, pin K of J7-P7, pin a of Ill-P11, contacts 4 and 2of relay K1, to ground.

RECEIVE CONDITION: The associated equipment provides ground potential toincoming line 1 or 2 to signal the corresponding Unit 1 or Unit 2printer to receive. This simplex ground signaling operates relay Kl-l orKI-Z. Hence, if Unit 1 is to receive, line 1 is grounded and thefollowing events occur. Battery-connected relay Kl-l operates, andswitches the operating circuit for RECEIVE lamp DSS through contacts 2and 4 so that now only relay K1 controls the RECEIVE lamp. The RECEIVElamp remains on as a signal that a message will be sent to the set.Relay K1-1 energizes relays K2-1 and K3-1 from ground through itscontacts 6 and 1. Diode CR11, in the operating path of relay K31, willallow current to flow from contacts 6 and 1 of relay K1-1 to the coil ofrelay K2-1, but will block current flow in the opposite direction whenrelay K2-1 is 0perated by mode panel relay K3. Relay K2-1 then turns onthe printer motor of Unit 1. Relay K31 then connects the incoming signalline to the printer electronics through its contacts 6 and 1, anddisconnects the keyboard output circuit from the printer electronics.During the STORE mode (as will be explained hereinafter) relay K 31 isreleased to disconnect the incoming signal line from the printer whilethe keyboard is sending. The mark tone on the incoming line wouldotherwise prevent the printer from monitoring what is being sent by thekeyboard. At the end of the message, the associated equipment removesground potential from incoming line 1. Relays Kl-l, K21, and K3-1release, the printer motor B1 of Unit 1 turns off, and the RECEIVE lampDSS remains lighted.

STORE: To store a message in the recorder before sending to the outgoingline, the operator depresses and holds the REWIND pushbutton until thegreen start-oftape lamp lights momentarily. Operation of the STOREpushbutton now completes a circuit for relay K6 as follows: negative 28volts through RECEIVE switch S1, contacts 8 and 6 of relay K8, blockingdiode CR9, coil of relay K6, operated contacts of STORE switch S5,nonoperated contacts of switches S4 and S3, pin W of P11- J11, pin I ofP7-J7, contacts and 2 of relay K1-1, pin K of J7-P7, pin d of I11P11,contacts 4 and 2 of relay Kl, to ground. Relay K6 operates and turns oilthe RECEIVE lamp DSS through contacts 8 and 6; locks itself to the sameoperating ground that was used by the RE- CEIVE lamp through contacts 6and 1; and extends ground to the recorder to trigger the advanceone-shot through contacts 2 and 5. The STORE lamp D84 lights from thesame circuit that holds relay K6 operated. The recorder advances thetape a set amount to assure that any variation in the commutatorcontacts that light the start-of-tape Will not prevent recording fromstarting on a usable portion of the tape.

The same circuit that operates relay K6 also operates relay K3 asfollows, starting from ground already traced to terminal 7 of relay K6:diode CRlt), diode CR11, coil of relay K3, contacts 6 and 8 of relay K8,normally-closed contacts of the RECEIVE switch S1, to negative 2 8volts. Operated, relay K3 at contacts 1 and 6 completes a circuit fromthe keyboard output to the printer 102 input as follows: keyboardconnectors P14-J14 pin S, connectors J7-P7 pin S, mode panel connectorsIll-P11 pin C, contacts 6 and 1 of relay K3, connectors P11-J11 pin A,connectors P7J 7 pin A, contacts 8 and 6 of relay K3-1, to the printer102 electronics. This path allows the information being stored in therecorder to appear also on the printer 102 of Unit 1. Mode panel relayK3 operates power supply relay K2-1 through contacts 5 and 2 whichsupplies power to the motor B1 of printer 102. The same operatingcircuit used for relay K6 also operates the magnetic tape recorder relayKR1 via diode CRlt). Recorder relay KR1 prepares circuits to the recordhead windings 260 and 262.

To interrupt the STORE mode for an incoming message, the associatedequipment places ground potential on incoming line 1. Relay Kl-loperates; lights the RECEIVE lamp DSS through contacts 2 and 4; releasesrelays K6 and K3 through contacts 2 and 5; turns 011 the STORE lamp D54;and releases recorder relay KR1. Relay K1-1 holds relay K2-1 operatedthrough contacts 6 and 1 to keep the motor running, and operates relayK3-1 to connect incoming line 1 to the printer tone detector.

NO ADVANCE: To continue storing a message in the recorder after aninterruption to allow an incoming message to be received, the operatordepresses the NO AD- VANCE pushbutton. Operated, the NO ADVANCE switchS6 completes a circuit to relay K7 from the same ground that the STOREswitch S5 extended to relay K6, as has been explained hereinbefore.Relay K7 operates, lights the NO ADVANCE lamp DS7 through contacts 2 and5, turns oit the RECEIVE lamp DSS through contacts 8 and 6, and atcontacts 6 and 1 locks to the original 8 operating ground'frorn relay K1contacts 4 and 2. Note that the advance one-shot 240' in the recorderelectronics is not triggered as occurred in the previously describedSTORE mode. Relay K3 operates as in the STORE mode to turn on the Unit 1printer motor B1 and to connect the keyboard output to the printer 102.

REWIND AFTER STORE OR NO ADVANCE: After a message is stored, theoperator depresses the REWIND pushbutton. Mode panel relay K8 operatesthrough recorder transistor Q2 which is turned on by the operatedpushbutton switch. Relay K8 at contacts 8 and 6 releases relay K6 (STOREmode) or K7 (NO ADVANCE mode), and also releases relay K3. When rewindis completed, recorder transistor Q2 (see portion of recorderelectronics, lower right of FIGURE 5B) is turned off and relay K8releases.

SEND KEYBD: Before sending to the outgoing line, the operator depressesthe SEND KEYBD pushbutton. If the associated equipment is ready toassign a link to this station, ground potential is placed on theoutgoing line. Switch S2 extends this ground to relay K1. Relay K1 locksto the ground on the outgoing line through contacts 7 and 6, lights theSEND KEYBD lamp DS1 through contacts 2 and 5, and turns off the RECEIVElamp DSS through contacts 2 and 4. With the SEND KEYBD lamp DSll on, theoperator types the called stations call letters and then depresses theRECEIVE pushbutton. Relay Kl releases because the operated RE- CEIVEswitch S1 opens its circuit. Relay K1 disconnects negative 28 volts fromthe outgoing line through contacts 7 and 6 as a signal that the callletters have been sent. When the connection is established to the calledstation, a go-ahead signal is sent by the associated equipment to theprinter of Unit 1. The operator now depresses the SEND KEYBD pushbuttonagain and types the message or starts the recorder. The SEND KEYBDswitch S2 extends ground potential to relay K1. Relay K1 operates, locksto the outgoing line as before, and lights the SEND KEYBD lamp DS1.

SEND RECORD: After receiving a go-ahead signal, in the manner abovedescribed, the operator depresses the SEND KEYBD pushbutton to seize theoutgoing line. If the recorder is to send the message, the operator nextdepresses the SEND RECORD pushbutton. Switch S7 extends ground fromrelay K1 contacts 2 and 5 to relay K9 and to the SEND RECORD lamp DS6.Operated, relay K9 locks through contacts 1 and 6, and triggers therecorder search register 276 through contacts 2 and 5 to allow the tapeto be searched for the first character of the message. Relay K9 alsooperates recorder relay KR2 through contacts 2 and 5 to provide circuitsfor the recorder head playback windings 286, 282. Further, relay K9provides an inhibit level to the keyboard through contacts 2 and 5 toprevent keyboard sending even though a key is depressed by mistake. Whenthe recorder reaches the end of the stored message, the blank tape thatfollows the message will stop the tape movement. The operator on notingthe end of the message on the printer 102 of Unit 1, or on noting thatthe sound of recorder operation has ceased, can depress the REWIND ORRECEIVE pushbutton.

If the REWIND pushbutton is depressed, relay K8 opcrates through thecircuit previously described, and releases relay K9 and turns off theSEND RECORD lamp DS6.

If the RECEIVE pushbutton is depressed instead of the REWIND pushbutton,relay K1 releases, releasing relay K9 through contacts 6 and 7, andturning off the SEND KEY BD lamp DSl through contacts 2 and 5.

KEYBOARD UNIT CIRCUIT FUNCTIONING: The block diagram description belowrefers to FIGURE 6 and expands on the general description of thekeyboard as has been presented hereinbefore. The mechanical keyboardstructure will be fully described in a later section.

TYPING KEYS: A depressed typing key 130 or space bar 460 triggers thefollowing operations:

(1) Contacts of a U-bar reed switch 148 close and set a counter inputgate register 210.

(2) Contacts of a pulse-per-character switch 212 close and trigger acharacter counter one-shot 214 energizing a counter stepping solenoid216. The pulse-per-character switch 212 close each time a character keybutton is depressed to cause the receiving printer 102 to either printand space or just to space. When closed, the switch 212 triggers thecharacter counter one-shot 214 to energize the counter solenoid 216 longenough to advance the character counter 122 one index step.

(3) The contacts of one to five reed code switches 146:1-146e close,depending on the Baudot code of the typed character. The ground levelsprovided by these switches 146 set a parallel register group 218 after a7 to 10 millisecond time delay. This delay is provided by a read delayone-shot 220 and guarantees that the reed contacts code switches 146will stop vibrating before the indicated character is gated into theparallel register group 218.

COUNTER INPUT GATE 210 is set by each typed character. In being set, theregister 210 (a) triggers the read delay one-shot 220, ('b) sets akeyboard lock register 222, and provides a level that will allow anoutput pulse from a 3-stage divider 224 to step a 3-stage counter 226.After countdown is completed by the counter 226, it resets the counterinput gate 210 via a flip-flop register 228 called a counter input gatereset.

KEYBOARD LOCK MECHANISM 123: The code bails of the keyboard, as will bedescribed hereinafter, are locked momentarily each time a depressedtyping key moves them to encode the corresponding character. Thekeyboard lock register 222, set by the counter input gate 210, operatesa lock solenoid 230 to perform a mechanical locking operation by meansof a lock plate (see FIGURE 21) to be later described. When twocharacters are typed in rapid succession, such that the line rate isexceeded, the first character is transmitted and the second characterwill be held locked in mechanical storage in the keyboard 106 until thefirst character is completely transmitted electrically. In addition toeffecting mechanical storage, the lock mechanism 123, by preventingmovement of the code bails, also prevents depression of any other typingkey.

When the recorder 108 is sending and at other times when it is necessaryto prevent use of the keyboard, inhibition of the keyboard is notaccomplished by the lock mechanism 123. Rather, input from the U-barreed switch 148 to the counter input gate 210 is inhibited electricallyas will be hereinafter more fully described.

READ DELAY ONE-SHOT 220 is triggered by the counter input gate 210.After the 7- to lO-millisecond delay designed into the circuit, theone-shot 220 gates the output of the code switches 146 into the parallelregister group 218.

FREQUENCY STANDARD 232: Two are used, one for 60 w.p.m. and one for 100w.p.m., and whichever standard is used, a tuning fork oscillator locatedin the power supply unit 110 provides pulses continuously at a rate thatdoes not vary more than :.01 percent. The output frequency of theselected frequency standard 232 is divided down by the S-stage divider224 so that every eighth pulse from the standard steps the 3-stagecounter 226. A character stored in the parallel register group 218 by adepressed keyboard key, or alternatively by the tape recorder 108, isgated sequentially into a IZOD-cycle astable multivibrator 234 by the3-stage counter 226. This free-running multivibrator 234 supplies the1200- cycle tone used for signaling on the outgoing line and is turnedon and off by the 3-stage counter 226 via a set of parallel-to-serialgates 227.

When sending is initiated by a depressed typing key,

10 the counter 226 is started by the counter input gate 210. At the endof countdown, the counter 226 resets the counter input gate 210 via thecounter input gate reset register 228.

When sending is initiated by the magnetic tape recorder 108, the counter226 is started by a playback time base gate 236. At the start ofcountdown, the counter 226 signals the recorder (via A B C to move themagnetic tape one character step.

Basic circuits and logic symbols FIGURE 7 shows the basic circuits andcorresponding logic symbols used in the keyboard logic diagram of FIGURE8. This section includes a description of each basic circuit and thecorresponding logic symbol, and the immediately following sectionsexplain the switching logic of the printer, keyboard, and recorder asshown on related logic and timing diagrams.

Positive-going transitions are used to transfer information from onetransistor stage to another. Logic 1 is defined as zero or groundpotential; logic 0 is defined as negative or minus 12 volts potential.Therefore, a positive-going transition is a rapid change from logic 0 tologic 1. This change is available at the collector of a transistor as itis driven from the otf state to saturation. Inthe transistorize'dcircuitry of this invention, a positive transition (that is, positivepulse) will turn off a transistor to set or reset a register or totrigger a one-shot.

The logic symbols shown on FIGURE 7 provide both a logic and a blockdiagram representation of the circuit shown at the left of the symbol.Input and output leads are designated A, T, Q, etc. on both the circuitand logic symbol to allow exact interpretation. The following [pointsmust be understood: (1) If a stage inverts the input signal, the outputlead leaves the symbol in a vertical direction as shown in FIGURE 7,blocks A, B and H. (2) The basic logic symbol for flip-flop stages showsthe set state. The upper square of the symbol is always marked 1; theinput lead is the setting input; the output lead is the collector of thetransistor that is turned on and, therefore, goes to logic 1 as thestage is set. Similarly, the lower square of the symbol is always marked0; the input lead is the reset input; the output lead is the collectorof the transistor that is turned off by the setting pulse and that,therefore, goes to logic 0 as the stage is set. (3) An inhibiting inputis marked with a circle as shown in FIGURE 7, block E, lead I.

INVERTER: FIGURE 7, block A shows an inverter or amplifier. The samesymbol enlarged with the letters HP (high power) is used on FIGURE 8 fordriver stages that energize solenoids. Transistor Q1 is normally on dueto the forward *bias -12 volts which is suflicient to override thereverse bias of the +5 volts. A logic 0 on lead A will not change thestate of the circuit; therefore, the output on lead T is logic 1. Alogic 1 on lead A will block the 12 volt forward bias and allow the+5-volt reverse bias to turn off transistor Q1. With transistor Q1turned off, a logic 0 is present on output lead T.

PEDESTAL GATE: FIGURE 7, block B shows a pedestal gate, so named becausea positive level on input lead A raises the voltage swing used totrigger via input lead B to the point where it can turn off atransistor. Pedestal gates are used extensively since they are soflexible. For example, a triggering pulse can be blocked by having anegative level rather than a positive level on the A input lead.Further, information available as a level can be stored on the gate, tobe used at a later time when the triggering pulse is supplied. The diodein the output of a pedestal gate blocks the negative pulse that isinherent in the differentiating action of the circuit. Pedestal gatesthat are primarily differentiating networks have the A input resistoralways at ground potential and are so shown on the printer, keyboard,and recorder logic diagrams.

DELAY: FIGURE 7, block C shows the circuit and associated logic symbolused to provide a short delay. Longer delays are provided by one-shotsas described below for block L. Transistor Q1 is biased on by the l2volts present at its base through resistor R1. A positive pulse on leadA turns off transistor Q1. Transistor Q1 remains off until capacitor C1discharges through resistor R1. The length of the delay is determined bythe value of resistor R1 and capacitor C1.

SINGLE DIODE GATE: FIGURE 7. block D shows a diode gate that has onlyone input. The function of the gate is to pass only positive pulses andto block negative pulses.

OR GATE: The truth table in FIGURE 7, block F shows that the output ofan OR gate is ,logic 1 (positive) when any one input is logic 1. Withall of the inputs at logic (negative), the output is also at logic 0. Achange of any one input to logic 1 provides a positive triggering pulse.FIGURE 12 shows OR' gates used as machine function detectors (OR gates0R2, ORS, OR11, OR12, OR13, and OR14). These gates provide a logic 0level that allows a triggering pulse to set a corresponding one-shot.NOR GATE: FIGURE 7, block G shows a NOR (not OR) gate that is the sameas an OR gate except that the output of the OR portion is fed through atransistor to invert the output.

OR GATE WITH INHIBITOR: FIGURE 7, block B.

shows an OR gate. with an inhibiting input. 'With logic 1 applied by theinhibitor, it is impossible to produce an output transition form 0 to 1since the output is always at l. I

AND GATE: The truth table in FIGURE '7, block I shows that the output ofan AND gate is logic 1 only when all inputs are logic 1.

NAND GATE: FIGURE 7, block H shows a NAND (not AND) gate that is thesame as an AND gate except that the output of the AND portion is fedthrough a transistor to invert the output.

REGISTER: FIGURE 7, block K shows a flip-flop register that is used as atemporary storage component. When voltage is initially applied to thecircuit, one of the transistors conducts first due to circuit valueimbalance. Assuming transistor Q1 turns on, its collector approachesground. The current from volts through register R4, resister R2, and thecollector-emitter junction of Q1 places a level of approximately +2volts at the base of transistor Q2, insuring its cut-01f. A positivepulse applied to lead S is passed by diode CR1 and turns ofl transistorQ1. The collector of Q1 goes to -12 volts which is present through thecross-coupling resistor R2 to the base of transistor Q2, causingtransistor Q2 to turn on. When transistor Q2 turns on, its collectorapproaches ground. The current from +5 volts through resister R3,resistor R5, and collector-emitter junction of transistor Q2 places alevel of approximately +2 volts at the base of transistor Q1, reversebiasing it. A positive pulse at point R will pass through diode CR2 andturn off transistor Q2. This will flip the circuit back to its originalcondition. Alternate pulses at point S and point- R will flip thecircuit back and forth.

ONE SHOT: FIGURE 7, block L shown a one-shot that is used as an accuratetiming device. When voltage is initially applied to the circuit,transistor Q1 is on due to the forward bias provided through resistorR4, and transistor Q2 is off due to the reverse bias provided throughresistor R5. With transistor Q1 on, capacitor C1 charges from 20 voltsto ground through resistor R6,=

resistor R3, and the base-emitter junction of transistor Q1. Whencapacitor C1 is fully charged, it has no efiect on the state of thecircuit as long as transistor Q1 is on. When a positive pulse comes inat point A it is passed by diode CR1 and turns ofi transistor Q1provided the pulse has enough amplitude to override the 0.35-volt levelpresent at the base.

When transistor Q1 goes off, its collector goes to ap- R2, causingtransistor Q2 to come on. Lead Q1 goes to the base of a solenoid drivertransistor. Transistor Q2 conducts through the base-emitter junction ofthe driver transistor to ground. With transistor Q2 on, the negativepotential at its collector is switched common to its emitter and ispresent at the base of the solenoid driver transistor, causing it to goon. When transistor Q2 comes on, its collector approaches ground, thusreferencing the charge on capacitor C1 to ground. The positive side ofcapacitor C1 is now +20 volts with respect to ground. Capacitor C1 nowattempts to discharge and recharge to 20 volts through resistor R4 fromthe emitter-base junction of transistor Q2 and the emitter-base junctionof the solenoid driver transistor. When the capacitor passes through.zero potential and begins to accumulate a negative charge, it turns ontransistor Q1.

When transistor Q1 conducts, its collector approaches ground, allowingthe +5-volt bias through resistor R5 to turn off transistor Q2. The timeinvolved for capacitor C1 to discharge, to .zero volt and to accumulateenough negative charge to turn on transistor Q1 is determined by thevalue of resistor R1 and the value of C1. This R-C time determines theduration of the output pulse on lead Q1.

COUNTER OR DIVIDER: FIGURE 7, block M shows a counter stage. It is alsoa divider stage when used to divide down the output of the keyboardfrequency standard. When voltage is initially applied to this circuit,one of the transistors will conduct due to circuit value imbalance.Assuming transistor Q1 conducts, its collector is at 0.15 volt withrespect to ground. This potential is present through resistor R2 at theanode of diode CR1. Since transistor Q2 is off, volts is present at itscollector and this potential is present through resistor R8 and at theanode of diode CR2.

When a positive pulse comes in at point S,.it passes through capacitorC1 and capacitor C2. Since diode CR2 has a large negative potential atits anode, it blocks the pulse. Diode CR1 passes the positive pulse,provided the pulse is large enough to override the 0.15 volt present atthe anode. In order to turn off transistor Q1, the pulse must also be ofsufiicient amplitude to override the -0.35-v0lt potential at the base oftransistor Q1. When transistor Q1 turns off, its collector goes toapproximately 10.5 volts due to the 1.5-volt drop across resistor R1.This 1.5-volt drop is due to the small current from l2 volts throughresistor R1, resistor R3, and resistor R5 to +5 volts. The base oftransistor Q2 is now at approximately 5.6 volts and therefore turns on.With transistor Q2 on, its collector is at 0.15 volt and the collectorof transistor Q1 is at 10.5 volts. This minus voltage is present throughresistor R2 and is at the anode of diode CR1. The 0.l5 volt at thecollector of transistor Q2 is present through resistor R8 and is at theanode of diode CR2.

The next positive pulse at point S will be blocked by diode CR1 andpassed by diode CR2. Transistor Q2 now goes ofl? and transistor Q1 comeson. Successive positive pulses at point S will trigger transistor Q1 andtransistor Q2 alternately.

FREE-RUNNING MULTIVIBRATOR: FIGURE 7, block N shOWs an astable offree-running multivibrator that is used as a timing standard whenextreme accuracy is not required. When the supply voltage is present andprovided point A is at ground potential, the multivibrator will start tocycle. Component value tolerances are such that there will be animbalance, enough such that one transistor will conduct first. Assumingtransistor Q1 conducts first, capacitor C2 will charge through resistorR4 and the base-emitter junction of the transistor Q1. Capacitor C2charges to the potential at the base of transistor Q1 which isapproximately 0.35 volt with respect to ground. Since capacitor C1 hasdischarged

1. A KEYBOARD TRANSMITTER COMPRISING: MANIPULATIVE MECHANICAL KEYBOARDSTRUCTURE AND TRANSMISSION COMPONENTS CONTROLLED THEREBY, SAID KEYBOARDSTRUCTURE INCLUDING: A PLURALITY OF SHIFTABLY DEPRESSIBLE KEY LEVERS; APLURALITY OF LONGITUDINALLY PIVOTED CODE BAILS WITH COOPERATING PORTIONSOF SAID KEY LEVERS AND CODE BAILS INCLUDING ABUTMENTS AND PERMUTATIVELYARRANGED NOTCHES ENABLING POSITIVE ENGAGEMENT BETWEEN EACH DEPRESSED KEYLEVER AND ALL CODE BAILS TO PROVIDE OPERATION OF EACH OF SAID CODE BAILSTO AND RETENTION IN EITHER ONE OF ONLY TWO PIVOTAL POSITIONS, UPONACTUATION OF A KEY LEVER, REPRESENTATIVE OF A MARK, OR A SPACECONDITION, SAID PIVOTALLY POSITIONED CODE BAILS THEREUPON PROVIDING ASPECIFIC PERMUTATION CODE CORRESPONDING TO THE CHARACTER ON SAIDDEPRESSED KEY LEVER; A UNIVERSAL BAIL INVARIABLY ENGAGED BY AND OPERATEDUPON DEPRESSION OF ANY KEY LEVER; A PLURALITY